Chapter 13: Section 3

Learning TargetsDescribe the difference between a real and a

virtual imageDraw ray diagrams for objects located at

various distances from concave mirrorsDraw ray diagrams for objects located at

various distances from convex mirrors

Curved vs. Flat MirrorsImages formed by curved mirrors

differ from those formed by flat mirrorsDepending on the object location, the

image could be enlarged or reduced in size

The image could also be inverted or upright

Concave Spherical MirrorsA spherical mirror with light reflecting

from its silvered, concave surface, is called a concave mirrorConcave mirrors are capable of forming

both real and virtual images

What is a Real Image???A reflected image that appears to lie in front of

the reflecting surface is called a real imageThis is in contrast to a virtual image which

appears behind the mirror. When a real image is produced, that image can

be obtained on a screen placed in front of the mirrorhttp://www.youtube.com/watch?v=KVpSCICCD9A

Ray Diagrams for Concave MirrorsThere are two rules of reflection for

concave mirrors. Any incident ray traveling parallel to the

principal axis will pass through the focal point upon reflection.

Any incident ray passing through the focal point will travel parallel to the principal axis upon reflection

Real or Virtual?Real images are formed when:

Objects are located behind the center of curvature

Objects are located at the center of curvature

Objects are between the center of curvature and the focal point

Virtual images are formed when:Objects are located in front of the

focal point

If an object is located at the focal point, the reflected rays never cross.Therefore no image is formed

Concave Mirror Practice

Convex Spherical MirrorsThe passenger’s side mirrors on a car

bulge outward at the centerImages in this mirror are distorted near

the mirror’s edges, and the image is smaller than the object

This type of mirror is called a convex spherical mirror

Convex mirrors are also called diverging mirrors because incoming light rays diverge after reflection The resulting image is always virtual

Negative Focal LengthFor a convex mirror, the center of

curvature and the focal point are located behind the mirror.

Since the focal point is located behind the convex mirror, such a mirror is said to have a negative focal length value

Convex spherical mirrors take the objects in a large field of view and produce a small imageThis makes them well suited for providing

a complete view of a large areaThey are often placed in stores or busy

hallways

Ray Diagrams for Convex MirrorsAny incident ray traveling parallel to the

principal axis will reflect from the mirror and its extension will pass through the focal pointThis extension is represented by a dashed line

Any incident ray traveling towards a convex mirror such that its extension passes through the focal point will reflect and travel parallel to the principal axis

Image for Convex MirrorsLocated behind the convex mirror

A virtual imageAlways uprightReduced in size (i.e., smaller than

the object)

The diagram below illustrates that as the object distance is decreased:the image distance is decreased the image size is increased

So as an object approaches the mirror, its virtual image approaches the mirror and becomes larger.

Convex Mirror Practice